The present application relates to a battery pack containing therein a battery such as, e.g., a nonaqueous electrolyte secondary battery, and a manufacturing method therefor. More particularly, the present application relates to a battery pack having a battery obtained by packing a battery element, which is formed by winding or laminating an anode and a cathode through separators, with a packing member, and a manufacturing method therefor.
In recent years, many portable electronics, such as camera-incorporated video tape recorders, portable telephones, and portable computers, have been marketed, and efforts have been made to make them smaller and lighter.
As electronics become small and light, a battery pack used as their portable power supply demands not only high energy but also smaller size and lighter weight. Among batteries used for such a battery pack is a lithium ion secondary battery having high capacity.
In the lithium ion secondary battery, a battery element having an anode and a cathode capable of doping/dedoping lithium ions is sealed in a metallic can or a metallic laminate film, and control is performed by a circuit board electrically connected to the battery element.
Furthermore, some related-art lithium ion secondary batteries are configured such that a lithium ion secondary battery is encased in a casing vertically split into two parts, together with a circuit board to form a battery pack (see, e.g., Japanese Patents Nos. 3556875, 3614767, and 3643792).
By the way, in related-art lithium ion secondary batteries such as mentioned above, those using the metallic can for sealing the battery element can easily ensure high dimensional accuracy, but are slightly thicker and heavier.
Meanwhile, those using the metallic laminate film for sealing the battery element are thinner and lighter than those using the metallic can, but have shortcomings that it is difficult to increase the dimensional accuracy due to large variations in the size of the battery element, and hence that their mechanical strength is low.
Furthermore, in those related-art battery packs in which the lithium ion secondary battery and the circuit board are encased in the casing, the casing need be thick enough to protect the lithium ion secondary battery and the circuit board from external shock and the like.
In addition, even in bonding the vertically split parts of the casing with a double-sided adhesive tape, by ultrasonic fusion-bonding, or the like, the casing need be thick enough to accommodate these methods. Hence, the thickness and weight of the battery pack as a whole increase, thereby imposing an issue that such batteries are not suitable as the portable power supply.
In coating a resin integrally on surfaces of a battery as a packaging material, a metallic can and the resin are integrally molded using molds, as disclosed in, e.g., Japanese Patents Nos. 3556875, 3614767, and 3929839.
However, there have been three roughly identified issues: (a) when a film-shaped packing member is used instead of a metallic can, the packing member as a middle member has a large dimensional tolerance so that its positioning is difficult; (2) the strength of the packing member is inferior so that injection pressure cannot be increased during molding; and (3) the film-shaped packing member for which an aluminum laminate film is typically used has its surface formed of nylon, a resin, such as polyethylene terephthalate, polypropylene, or the like, so that it is not easily bondable to the resin for molding.